Tableted detergents having improved green strength



Jan. 21, 1969 R. s. COOPER ET AL 3,423,322

TABLJETED DEIERGEN'I'S HAVING IMPROVED GREEN STRENGTH Filed July 23, 1964 VARIABLE VARIABLE FORCE FORCE G REEN STRENGTH 7., T KPP ADDED TO FORMULATION FIG. 3

INVENTORS ROBERT s. COOPER ALLEN D. URFER United States Patent Office Claims ABSTRACT OF THE DISCLOSURE Tableted detergents having improved green strength are prepared by incorporating with a sodium tripolyphosphate builder and synthetic surfactant from about 0.17% to about 6% of a potassium pyrophosphate or polyphosphate.

This invention relates to tableted kietergent compositions and more particularly to detergent compositions which have a high degree of strength immediately after tableting.

Tableted detergent compositions presently produced are known to be initially weak after being tableted, tending to break, chip, or crumble during subsequent handling operations. Upon standing, the tablets normally undergo a rapid increase in strength until they are able to withstand vigorous handling, usually within one hour after compression. Unfortunately, in most commercial tableting operations the tablets must be transported and otherwise handled prior to development of their ultimate strength. Tablet strength is particularly significant in operations where an appreciable amount of scrap material (from defective tablets previously produced, etc.) is recycled and combined with virgin granular detergent ingredients prior to tableting the same. Tablets prepared from ingredients containing a large amount of recycled scrap material tend to have lower initial strength, and, in turn produce more scrap which must be ground up and recycled, and so on. This initial tablet strength is measured and alternatively referred to herein as green strength.

We have now discovered that detergent tablets containing a small amount of a potassium pyrophosphate or polyphosphate have excellent initial strength and high resistance to cracking, chipping, or crumbling (disintegrating). In many cases the initial strength of the tablets may be doubled by the addition of the potassium phosphates of the invention. Further, the potassium phosphate may be added directly to formulations containing either anionic or nonionic detergents without otherwise modifying such formulations. An even further advantage is that the potassium pyrophosphates and polyphosphates are excellent detergent builders which will contribute to the cleaning properties of the detergent tablet.

For the purposes of the following description, the eX- pression green strength is defined as a measure of the compressive force, reported in grams, required to split or otherwise disintegrate a detergent tablet (1.75 in. dia. and 0.72 in. thick) immediately after formulation (within five minutes after tableting) when applied as illustrated schematically in FIGURES 1 and 2 of the appended drawing. Turning now to the drawing, FIGURE 1 shows a detergent tablet 10 being compressed between a fixed support 12 and a piston 11. A variable force indicated by the arrow in FIGURE 1 is gradually applied through the piston 11. This force is increased until the tablet breaks or crumbles, at which point the force, in grams, is noted and reported as green strength. FIG- URE 2 is a side view of FIGURE 1 illustrating a typical break 13. In some instances, especially where very low 3,423,322 Patented Jan. 21, 1969 green strength is observed, the tablets will fracture into several pieces and/or crumble.

Preferred potassium pyrophosphates and polyphosphates for use by the present invention are tetrapotassium pyrophosphate .(K P O' and potassium tripolyphosphate (K P O the pyrophosphates and polyphosphates being referred to hereinafter generally as simply potastium phosphates. the tetrapotassium pyrophosphate is particularly preferred since at nominal levels, it produces excellent improvement in green strength. Further, at such nominal levels, tetrapotassium pyrophosphate (alternatively denoted TKPP) furnishes somewhat greater improvement in tablet green strength than an equivalent weight of potassium tripolyphosphate (alternatively denoted KTPP). Potassium acid pyrophosphates and polyphosphates such as tripotassium acid pyrophosphate, dipotassium acid pyrophosphate, tripotassium acid tripolyphosphate as well as mixed salts such as tetrasodium potassium tripolyphosphate, trisodium dipotassium tripolyphosphate, and disodium dipotassium pyrophosphate are also among the potassium phosphates useful according to the invention. The potassium metaphosphates and orthophosphates are normally less effective than the pyrophosphates and tripolyphosphates in improving green strength, as will be illustrated by specific examples furnished at a later part of the present specification.

The amount of potassium phosphate which may be added to the detergent formulation must be critically controlled since higher amounts will, surprisingly, reduce green strength below that attainable without a potassium phosphate. This criticality can be illustrated by the fact that while 4% by weight of TKPP will nearly double green strength, an 8% level will yield tablets having a green strength of about half that obtainable without a potassium phosphate. Turning now to FIGURE 3 of the drawing, the effect of different percentages of added TKPP on the green strength of tablets prepared from a standard formulation may be readily seen. The standard detergent "formulation consisted of 60% sodium tripolyphosphate, 14% sodium sulfate, 10% Triton X-, (a surfactant), 15% sodium metasilicate, and 1% carboxymethyl cellulose, all percentages by weight. To accommodate the added TKPP, an equivalent weight of sodium sulfate was withheld from the formulation. The graph of FIGURE 3 indicates that as TKPP content is increased in the formulation by small amounts, up to about 4% by weight of the total, a pronounced increase in green strength occurs. At levels greater than 4%, green strength diminishes, rapidly between about 4% and 6% and more slowly after 6%. A similar result occurs when potassium tripolyphosphate or the other potassium phosphates are used, although the amount necessary to produce maximum improvement will vary from compound to compound.

For maximum improvement of green strength, tetrapotassium pyrophosphate will normally comprise between 0.1% and 5.0% by weight of the tableted detergent composition, and preferably between 0.2% and 4.0% by weight. Likewise, the amount of potassium tripolyphosphate which may be added to improve green strength must be critically controlled, but at higher levels than allowable for T'KPP. The preferred level of potassium tripolyphosphate is between about 0.5% and 6.0% by weight of the total formulation, although from 0.2% to about 8.0% represents the broader limitation. Other potassium pyrophosphates can be added at about the same levels as the tetrapotassium pyrophosphate while other potassium polyphosphates perform best at the levels suitable for potassium tripolyphosphate.

The detergent tablets of the invention will comprise, in addition to the amounts of potassium phosphate mentioned above, between 30% and 80% by weight of sodium tripolyphosphate and between and 25% by weight of a synthetic, non-soap, anionic or nonionic surfactant. Further ingredients which may be used with the foregoing major components are the various alkali metal silicates, sulfates, orthophosp'hates, and carbonates as well as the conventional inorganic and organic auxiliary materials such as fillers, binders, corrosion inhibitors, anti-redeposition agents (typically carboxymethyl cellulose), suds builders, tarnish inhibitors, foam stabilizers, foaming agents, fluorescent brightening agents, bacteriostatic agents, perfumes, coloring matter, preservatives, and the like. In usual practice the silicates, sulfates, orthophosphates, carbonates, and inorganic and organic auxiliary materials will comprise between 1% and 30% by weight of the total detergent composition. Suitable anionic and nonionic surfactants include water soluble salts of organic sulfuric reaction products having in their molecular structure an alkyl or acyl radical and a sulfonic acid or sulfuric acid ester radical, compounds containing a water solubilizing polyoxyethylene group chemically combined with an organic hydrophobic compound, and alkyl phosphate surfactants. The surfactant may be biodegradable or nonbiogradable. Further, the tableted detergents may contain a small amount, up to about %by weight of water, which may be added before or after tableting. A preferred water content for the tableted detergents is between about 2% and 5% by weight.

The tableted detergent compositions are produced by methods well known in this art. For example, prior to tableting, the dry ingredients may be physically admixed after which the liquid ingredients are sprayed or otherwise applied to an agitated bed of the mixture. A homogeneous mixture such as that obtained by spray drying or roll drying an aqueous slurry of the ingredients may also be used. Tableted compositions are prepared from the final mixture of ingredients by compressing the same under a pressure of usually between 30 p.s.i. and 300 p.s.i. and thereafter curing or treating the tablets to develop final strength. The requirement for after-treating or curing of the tablet is, however, not essential, but may be desirable where greater tablet strength is thought desirable.

The potassium phosphate may be added to the other detergent ingredients in a variety of ways, all of which are satisfactory for enhancement of green strength. Perhaps the most obvious method of addition comprises simply dry mixing powdered potassium phosphate with the other detergent ingredients prior to tableting. An equally satisfactory method comprises preparing an aqueous solution of the potassium phosphate and spraying this upon an agitated bed of the other ingredients.

A particularly preferred procedure for incorporating the potassium phosphate in the final detergent tablet involves preparing what may be termed an intraparticulate mixture (as distinguished from a simple mechanical mixture) of potassium phosphate and sodium tripolyphosphate and adding such mixture to the other detergent ingredients by methods well known heretofore in the preparation of tableted detergents. Surprisingly, such mixtures are free-flowing and do not appreciably cake, while potassium phosphates in their uncombined state can have a pronounced capacity for absorbing atmospheric moisture and caking and usually require special containers for storage and shipment. Consequently, these mixtures furnish the manufacturer of tableted detergents an advantageous alternative to the difficult handling problems which might be encountered when formulating with such hygroscopic compounds as tetrapotassium pyrophosphate. The intraparticulate mixtures may be prepared, perhaps most efficiently, at the sodium tripolyphosphate manufacturing site and stored and shipped in containers regularly used for sodium tripolyphosphate, thus obviating the expensive packaging requirements for hygroscopic materials. Also the segregation problems attending mechanical mixtures are not encountered with the present mixtures which are uniform. Manifestly, such mixtures furnish a most feasible avenue for efiicaciously accomplishing the objectives mentioned herein and are therefore thought to be an important and integral facet of the invention.

Depending upon the particular mode selected for preparing the intraparticulate mixtures, the potassium phosphate will either be occluded within, or near the surface of the sodium tripolyphosphate particles. One method for incorporating the potassium phosphate comprises adding a potassium compound to the starting materials used in the manufacture of sodium tripolyphosphate. Thus potassium pyrophosphate may be added to a mixture of monosodium orthophosphate and disodium orthophosphate having an Na O:P O ratio of about 1.67 before conversion of the same at elevated temperatures to form sodium tripolyphosphate. A typical procedure for producing tripolyphosphate from the mixed orthophosphate salts is disclosed in US. Patent 2,977,317. A similar result may be achieved where a potassium orthophosphate, e.g., dipotassium phosphate or a potassium-containing base, e.g., potassium hydroxide is included with the starting materials before conversion. Prepared by this latter variation, however, the mixtures tend to comprise, due to molecular and intermolecular dehydration of the potassium compounds, some of the less effective (for improving green strength) potassium compounds such as metaphosphates, mixed salts, and polyphosphates, instead of all potassium pyrophosphates. Better in-process control and reduction of the distribution of the potassium into less effective compounds can be accomplished if the potassium compound is added initially in the form of a condensed phosphate, e.g., TKPP or KTPP. Such condensed phosphates, especially KTPP, do not undergo intermolecular dehydration with the sodium phosphates to the same extent as the potassium orthophosphates. To further reduce, or eliminate altogether, molecular and/ or intermolecular dehydration of the potassium compound it may be added to the sodium tripolyphosphate during or subsequent to conversion. One particularly desirable method comprises preparing a concentrated aqueous solution of TKPP (e.g., 60% TKPP solution) and spraying such solution upon a bed of sodium tripolyphosphate particles. Such solutions may be sprayed upon sodium tripolyphosphate while it is being produced in a dense fluidized bed or after its discharge from the bed. If the solution is added while the tripolyphosphate is still hot (e.g., 50350 C.) the water is quickly evaporated to yield a dry particulate product. Where the amount of added TKPP is within the range specified herein, the product is dry and free-flowing, and has about the same palpable physical properties as pure sodium tripolyphosphate while furnishing much greater green strength when used in tableted detergents.

The following specific examples will further illustrate the principles of the invention, but should not be interpreted as limiting the broader aspects of the invention.

Example 1 Standard formulation: percent by wt. Sodium tripolyphosphate 60.0

Sodium sulfate 14.0 Triton X 2 10.0 Star silicate 15.0 Carboxymethyl cellulose 3 1.0

Sodium tripolyphosphate content reduced in proportions to added potassium phospl1atecontr0l samples contained 0. 2 Triton X-100 is the trademark of a commerclal surfactant vls isooctyl phenyl polyethoxyethanol.

Where the expression Carboxymethyl cellulose is used herein, it is intended to refer to the sodium salt of (:zllhnX) methyl cellulose.

To the above ingredients was added 25% by weight of scrap, such scrap being prepared by pulverizing tablets previously formed by the same method and containing the same ingredients in the proportions illustrated in the above formulation. All dry ingredients including scrap and potassium phosphate were placed in a Hobart mixing bowl after which the liquid surfactant and then the liquid lose cohesion and fall apart. Disintegration rate was measured after the tablets had been permitted to stand for one to three days at room temperature. The tablets were placed in unagitated water maintained at 120 F. (average laundering temperature) and the time required for complete disintegration was recorded. The results are reported in the following table.

TABLE II.EFFECT ON VARYING PROPORTIONS OF TKPP IN TABLETED DETERGENTS Formulations (percent by weight) Tablet Ingredients:

Tetrapotassium pyrophosphate 0. 0 2. 0 4. 0 6. 0 8. 0 10. 0 Sodium tripolyphosphate 60.0 58.0 56. 0 54. 0 52. O 50.0 Sodium sulfate 14. 0 14. 0 14. 0 14. 0 14. 0 14. 0 Triton X-100 (surfactant) 10.0 10.0 10. 0 10. 0 10. 0 10.0 15. 0 15.0 15.0 15. 0 15.0 15. 0 1.0 1.0 1.0 1.0 1.0 1.0 2, 066 2, 290 2, 724 1, 706 1, 403 1, 224 1 1 2 2 2 2 2 2 1 Tablets containing 6-10% TKPP were found to be hard and disintegrate slowly; tablets containing 2% TKPP were not distinguishable from those containing no potassium compound with regard to disintegration rate.

2 Tablets hard.

silicate were added accompanied by vigorous mixing. Mixing was continued for about one or two minutes after the liquid ingredients were added. The mixture was then held for approximately an hour after which it was tableted. The weight of all tablets was maintained at 28.6102 grams/ tablet, the diameter at 1.75 inches, and the thickness at 0.72 inch. Immediately after tableting (within seconds) the tablet green strength was determined by the method explained hereinbefore. A total of three tablets of the same composition were tested and the arithmetic average of the observed values was recorded. These averages are reported in the following table.

Table I.Eifect of physical admixtures of various potassium phosphates on green strength scrap recycled) Tablet green strength Added potassium phosphate: (grams) None (control sample) 1493 Tetrapotassium pyrophosphate (1%) 2272 Tetrapotassium pyrophosphate (2%) 2520 Tetrapotassium pyrophosphate (3%) 2700 Tetrapotassium pyrophosphate (4%) 3005 Monopotassium phosphate (2%) 1726 Dipotassium phosphate (2%) 1932 Tripotassium phosphate (2%) 1949 Potassium metaphosphate (2%) 1645 Potassium tripolyphosphate (2%) 2247 Example 2 Tablets were prepared to contain various amounts of TKPP and the usual detergent ingredients and proportions thereof set forth in the standard formulation of Example 1. Also, exactly the same method of mixing the ingredients and testing the resulting tablets were employed for this experiment. In addition to testing the tablets for green strength, each tablet was evaluated to determine its disintegration rate in water, i.e., not rate of solution, but rather the time required for the detergent particles to EXAMPLE 3 Tablets were prepared containing minor amounts of TKPP together with the usual detergent ingredients and proportions thereof shown in the foregoing examples. The ingredients were mixed, tableted, and the tablets were tested for green strength by the method shown in Example 1. The results were as follows:

Table III.-Etfect of minor proportions of TKPP in tableted detergents Amount of TKPP added to standard formulation, percent:

Tablet green strength (grams) Detergent tablets containing various proportions of sodium tripolyphosphate, both with and without tetrapotassium pyrophosphate, were prepared. These tablets were tested to determine what effect, if any, the sodium tripolyphosphate content has upon green strength, and also how such content influences any enhancement of green strength obtainable by the inclusion of a potassium compound. In preparing the mixtures for tableting, sodium tripolyphosphate (and any TKPP added) was mixed with sodium sulfate after which liquid Triton X- and then Star silicate were added with mixing. A small amount of water was sprayed upon the mixture, followed by a room temperature storage period of 0.5 to 1.5 hours, terminated by tableting the aged mixture. Green strength, reported in the table immediately below, was determined in the manner described previously.

TABLE IV.EFFEGT OF VARYING PROPORTIONS OF SODIUM TRIPOLYPHOSPHAIE Formulations (percent by weight) Tablet Ingredients:

Sodium tripolyphosphate 40.0 38. 0 50.0 48.0 60.0 58. 0 70.0 68.0

Tetrapotassium pyrophosphate 0 2.0 0 2.0 0 2. 0 0 2. 0

Sodium sulfate 33. 0 33.0 23. 0 23.0 13. 0 13. 0 3. 0 3.0

Triton X-100. 10. 0 10.0 10.0 10. 0 10.0 10.0 10.0 10.0

Star silicate 15.0 15. 0 15.0 15. 0 15. 0 15.0 15.0 15. 0

Water 2.0 2.0 2. 0 2.0 2.0 2.0 2. 0 2. 0 Green strength in grams (average of three tablets) 1, 512 2, 519 1, 773 2, 162 1, 840 2, 375 1,896 2,437

Example The main object of the experiments of this example was to study the effects upon green strength of variations of the types and proportions of common surfactants and/or the proportions of water, fillers, and other ingredients common to detergent tablet formulations (both with and without mechanically added TKPP). The detergent ingredients were mixed, tableted, and tested according to the procedures described in Examples 1 and 4 above and the findings are tabulated below.

Samples from each of the above lots were used as the builder ingredient in manufacturing detergent tablets according to the formulation and procedure described in Example 1, supra. By the procedure described in that example, scrap material was added to some of the tablets. All of the tablets were tested to evaluate their green strengths and the results of these tests are as follows:

Tablet green strength (grams) (average of Builder ingredient in tablets: three tablets) Lot 1 sample (no scrap or TKPP) 3114 Lot 2 sample (TKPP added, but no scrap) 3600 Lot 1 sample (25% scrapno TKPP) 2511 Lot 2 sample (25 scrap plus TKPP) 2902 Example 7 Sodium tripolyphosphate was prepared in accordance with the procedure described for lot 1 in Example 6, and divided into three separate samples (or lots). One sample was selected as a control and was therefore un- TABLE V.EFFECT OF VARYING COMMON INGREDIENTS IN TABLEIED DETERGENTS Formulations (percent by weight) Tablet Ingredients:

Sodium sulfate 0 0 27. 0 27. 0 28.0 28.0 0 0 27. 0 27.0 0 0 0 0 21.0 21. 0 Sodium tripolyphosphate l 50.0 48.0 45.0 43.0 50.0 48.0 60. 0 58.0 50.0 48.0 50.0 45.0 50.0 48.0 50.0 48. 0 Tetrapotassium pyrophosphate O 2.0 0 2.0 0 2.0 0 2.0 0 2.0 0 5. 0 0 2.0 0 2.0 Sodium carbonate 1 27.0 27.0 0 0 0 0 13.0 13.0 0 0 26. O 26.0 23.0 23.0 20.0 20.0 NazSiOa 5. 0 5. 0 8.0 8. 0 10.0 10.0 10.0 10.0 5. 0 5. 0 10.0 10.0 10.0 10.0 0 0 60 K 15.0 15.0 0 0 0 0 15.0 15.0 15.0 15.0 0 0 0 0 5.0 5.0 Triton X-100 3.0 3.0 0 0 10.0 10.0 0 0 3.0 3.0 10.0 10.0 0 0 0 0 Vietawet 208 0 0 13.0 13.0 0 0 0 0 0 0 0 0 0 0 0 0 Ultrawet K 0 0 0 0 0 0 0 0 0 0 0 O 15.0 15.0 0 0 Water 0 0 2- 0 2.0 2. 0 2.0 2.0 2.0 0 0 4.0 4.0 2.0 2.0 4. 0 4. 0 Powdered sodium tripolyphosphate 0 5. 0 5- 0 0 0 0 0 0 0 0 0 0 0 0 0 Tablet green strength in grams (average of three tablets) 1, 668 2, 528 1, 667 1, 98 1,234 1, 448 1, 628 1, 824 1, 548 2, 378 1, 610 2,137 1, 978 2, 360 1, 692 1, 930

1 Granular.

1 Powdered.

3 Trademark for a sodium alkyl aryl sulfonate-anionic surfactant.

4 glradenark for an ethylene oxide adduct of nonyl phenol-non-ionic sur actan Experiments directed to a comparison between the intraparticulate mixtures and simple mechanical mixtures of potassium phosphate and sodium tripolyphosphate are presented in the examples which follow.

Example 6 An intimate mixture of sodium phosphates (the usual feed for the manufacture of sodium tripolyphosphate) was first prepared as follows: A reaction mixture having an Na O:P O ratio of approximately 1.67 was formed by reacting soda ash and 87% H PO in the correct stoichiometric quantities. Sufficient water was removed from the reaction mixture by evaporation to result in a crystalline hydrate which, after evaporation of surface moisture, had about a 17% loss on ignition. The mixture was taken substantially dehydrated in a rotary drier at 100 C. to yield a somewhat porous material with about a 9% loss on ignition. This porous mixture of sodium phosphate salts was then divided into two lots, the first of which was hydrated by spraying water upon it until the loss on ignition was about 16% by weight. To the second lot was added an aqueous TKPP solution (8 lbs. of TKPP in 50 lbs. of city water) at a rate of 24 lbs. of solution for each 180 lbs. of phosphate salts. So prepared, the two lots were separately fed to a fluidized bed maintained at a temperature between 420450 C. where they were converted to sodium tripolyphosphate having the following analysis:

Lot 2 (TKPP-treated) Lot 1 (N0 potassium) 91.0% sodium tripolyphosphate. 3.0% sodium metaphospliate. 6.0% sodium pyrophosphate.

Trademark for a soidum dialkyl orthophosphatebiodegradable anionic surfactant.

6 aqueous solution.

7 Trademark for a sodium alkyl aryl sullonate-anionic surfactant.

treated, while to the second sample sufiicient TKPP was mechanically added to yield 2% by weight of TKPP in the final detergent formulation (the standard formulation of Example 1). The third sample was heated to 200 C. and then sprayed with a concentrated TKPP solution in an amount sufficient to furnish the same level of TKPP in the final detergent as the second sample mentioned herein. This sample was dried and cooled. Then the three were formulated in tableted detergent mixtures according to procedure described in Example 1. Upon running green strength tests the following results were discovered:

Tablet green strength (in grams) (average Detergent builder material used: of three tablets) Sample 1 (control-no TKPP) 2022 Sample 2 (2% TKPPmechanical mixture) 2657 Sample 3 2% TKPP-added from conc. solution) 2639 By a comparison of the observed green strength values, it is apparent that no significant chemical differences result from the different modes of applying the potassium phosphate. However, physical differences between the mechanical mixtures and those in which the TKPP was occluded within the porous tripolyphosphate were readily observed; the former tended to segregate and cake much more rapidly than the latter.

All of the cleaning compositions described and tested in accordance with the foregoing examples were evaluated by standard laboratory cleaning procedures and found to be equivalent or superior to similar compositions presently sold commercially for laundering and similar uses. Low density sodium tripolyphosphate (28-45 lbs/cu. ft.) was used in all formulations. Because of the variations in green strength normally occurring between sodium tripolyphosphates (when used as tableted detergent ingredients) produced by different methods and/ or at different times, each of the experiments reported herein included a control member selected from the same lot of sodium tripolyphosphate.

Potassium pyrophosphate or polyphosphate can also be incorporated in the detergent compositions of the invention by ion exchange technique. Suitable potassium donor compounds are the potassium salts and bases such as tripotassium orthophosphate, potassium sulfate, potasium carbonate, etc. To illustrate, potassium sulfate may be mechanically mixed with dampened sodium tripolyphosphate (e.g., treated with steam) to effect exchange between potassium and sodium. It should be noted that most commercial detergent grades of sodium tripolyphosphate contain small amounts, e.g., 2-6% by Weight, of tetrasodium pyrophosphate.

Computed on the basis of the weight of the sodium tripolyphosphate mixtures, the potassium pyrophosphates may comprise between 0.13% and 17% and preferably between 0.3% and 13% by weight of such mixtures. On this same basis, the allowable limits, by the present invention, on the amount of potassium tripolyphosphate in mixtures with sodium tripolyphosphate is between 0.25% and 27.0%, preferably between 0.6% and 20% by weight of such mixtures.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations are to be derived therefrom, as modifications will be obvious to those skilled in the art.

We claim:

1. A detergent tablet readily disintegrable in warm water and having improved green strength immediately after tableting comprising from 30% to 80% by weight of sodium tripolyphosphate, 5% to 25% by weight of a synthetic surfactant selected from non-soap organic anionic and non-ionic surfactants, and from about 0.1% to about 6% of a potassium phosphate selected from the group consisting of potassium pyrophosphate and potassium polyphosphate, said potassium phosphate being present in an amount sufiicient to effect said improvement in tablet green strength.

2. A detergent tablet readily disintegrable in warm water and having improved green strength immediately after tableting comprising from 30% to 80% by weight of sodium tripolyphosphate, 5% to 25% by weight of a synthetic surfactant selected from non-soap organic anionic and non-ionic surfactants and from 0.1% to 5% by weight of said tablet of a potassium pyrophosphate.

3. A detergent tablet readily disintegrable in warm water and having improved green strength immediately after tableting comprising from 30% to 80% by weight of sodium tripolyphosphate, 5% to 25% by weight of a synthetic surfactant selected from non-soap organic anionic and non-ionic surfactants, and 0.5% to 6.0% by weight of potassium tripolyphosphate.

4. A detergent tablet readily disintegrable in warm Water and having improved green strength immediately after tableting comprising from 30% to by weight of sodium tripolyphosphate, 5% to 25% by weight of a synthetic surfactant selected from non-soap organic anionic and non-ionic surfactants, and 0.2% to 4.0% by weight of tetrapotassium pyrophosphate.

5. A method of producing a non-hygroscopic, freeflowing intraparticulate mixture consisting of sodium phosphates and between 0.13% and 17% potassium phosphates suitable for use as the builder ingredient in detergent tablets which comprises preparing a concentrated aqueous solution of a potassium phosphate selected from the group consisting of potassium pyrophosphate and potassium polyphosphate, spraying said solution upon a bed of porous sodium tripolyphosphate particles, and thereafter removing any excess water from the resulting intraparticulate mixture.

6. The method of claim 5 wherein the potassium phosphate is tetrapotassium pyrophosphate.

7. The method of claim 5 wherein the potassium phosphate is potassium tripolyphosphate.

8. A method of producing a non-hygroscopic, freeflowing intraparticulate mixture consisting of sodium phosphates and between about 0.13% and 17% potassium phosphates suitable for use as the builder ingredient in detergent tablets which comprises reacting soda ash With concentrated orthophosphoric acid in stoichiometric quantities to furnish a mixture of sodium phosphates having an Na O:P O ratio of about 1.67, adding to said mixture of sodium phosphates a potassium phosphate selected from the group consisting of potassium pyrophosphate and potassium polyphosphate, and heating the resulting mixture for a time and at a temperature sufficient to convert substantially all of the sodium phosphates to sodium tripolyphosphate.

9. The method of claim 8 wherein the potassium phosphate is tetrapotassium pyrophosphate.

10. The method of claim 8 wherein the potassium phosphate is potassium tripolyphosphate.

References Cited UNITED STATES PATENTS 3,000,831 9/1961 Tuvel 25%-135 X 3,067,144 12/1962 Michaels 252 X 3,081,267 3/1963 Laskey 252135 3,133,024 5/1964 Feierstein et a1, 252-135 X 3,147,295 9/1964 Laughlin 252135 X 3,172,859 3/1965 Percival et al. 252-138 X 3,223,646 12/1965 McKenna et a1. 252-135 3,231,506 1/1966 Schulerud 252135 X LEON D. ROSDOL, Primary Examiner.

B. BETTIS, Assistant Examiner.

US. Cl. X.R. 252-137, 138 

